Erosion of top soil is a more significant problem than fertilizer. With respect to fertilizers and inorganic phosphate supply, it seems that these are not really necessary(they might actually be detrimental) as long as you provide the right soil microbiome for the crops which can outperform synthetic fertilization[1-2] (though I am very new to this and is outside my field and I am unsure of the validity of their claims).
[1] https://www.youtube.com/watch?v=cO2nGHq40Xc [2] https://www.youtube.com/watch?v=ErMHR6Mc4Bk
I think there is a big focus on "fossil fuels" but they are not the only resources we're using in an unsustainable way.